I am learning WPF animation, and I created a simple demo app with a pretty straightforward animation. I have divided the main grid into three rows; a Buttons Row at the top, and two content rows that for the remainder of the screen, one red and one blue. Complete XAML is below.
There are two buttons, Show Red and Show Blue. When each button is pressed, I want the area below the Buttons Row to change color with a slow top-to-bottom wipe. The Storyboard sets the height of both rows to 0, then animates the desired row to a height of 1*, like this:
<Storyboard>
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" From="0" To="1*" Duration="0:0:5" />
</Storyboard>
The colors change as expected, but there is no animation. So, my question is simple: Why isn't the animation working?
I am using a custom animation class, GridLengthAnimation (adapted from this CodeProject article) to animate the grid lengths. I have reproduced the class below.
To recreate the demo project: To recreate my demo project, create a new WPF project (I used VS 2010) and replace the XAML in MainWindow.xaml with the following:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Utility="clr-namespace:Utility" Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Name="Buttons" Height="35" />
<RowDefinition Name="RedRow" Height="0.5*" />
<RowDefinition Name="BlueRow" Height="0.5*" />
</Grid.RowDefinitions>
<!-- Buttons -->
<StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
<Button Content="Show Red" Width="100" Margin="5" >
<Button.Triggers>
<EventTrigger RoutedEvent="Button.Click">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" From="0" To="1*" Duration="0:0:5" />
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Button.Triggers>
</Button>
<Button Content="Show Blue" Width="100" Margin="5" >
<Button.Triggers>
<EventTrigger RoutedEvent="Button.Click">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" From="0" To="1*" Duration="0:0:5" />
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Button.Triggers>
</Button>
</StackPanel>
<!-- Grid Fills-->
<Border Grid.Row="1" Background="Red" />
<Border Grid.Row="2" Background="Blue" />
</Grid>
</Window>
There is no code-behind added to MainWindow.xaml.
Add a C# class to the project named GridLengthAnimation.cs. Replace the code in that class with the following:
using System;
using System.Windows.Media.Animation;
using System.Windows;
namespace Utility
{
/// <summary>
/// Enables animation of WPF Grid row heights and column widths.
/// </summary>
/// <remarks>Adapted from Graus & Sivakumar, "WPF Tutorial - Part 2 : Writing a custom animation class",
/// http://www.codeproject.com/KB/WPF/GridLengthAnimation.aspx, retrieved 08/12/2010.</remarks>
internal class GridLengthAnimation : AnimationTimeline
{
static GridLengthAnimation()
{
FromProperty = DependencyProperty.Register("From", typeof(GridLength),
typeof(GridLengthAnimation));
ToProperty = DependencyProperty.Register("To", typeof(GridLength),
typeof(GridLengthAnimation));
}
public override Type TargetPropertyType
{
get
{
return typeof(GridLength);
}
}
protected override Freezable CreateInstanceCore()
{
return new GridLengthAnimation();
}
public static readonly DependencyProperty FromProperty;
public GridLength From
{
get
{
return (GridLength)GetValue(FromProperty);
}
set
{
SetValue(FromProperty, value);
}
}
public static readonly DependencyProperty ToProperty;
public GridLength To
{
get
{
return (GridLength)GetValue(ToProperty);
}
set
{
SetValue(ToProperty, value);
}
}
public override object GetCurrentValue(object defaultOriginValue, object defaultDestinationValue, AnimationClock animationClock)
{
double fromVal = ((GridLength)GetValue(FromProperty)).Value;
double toVal = ((GridLength)GetValue(ToProperty)).Value;
if (animationClock.CurrentProgress != null)
{
if (fromVal > toVal)
{
return new GridLength((1 - animationClock.CurrentProgress.Value) * (fromVal - toVal) + toVal, GridUnitType.Star);
}
else
{
return new GridLength(animationClock.CurrentProgress.Value * (toVal - fromVal) + fromVal, GridUnitType.Star);
}
}
else
{
return null;
}
}
}
}
